A typical drawing application installed on a terminal, such as a smartphone or a tablet terminal, allows a users to write characters, draw pictures, etc., on a touch panel. In the following, a terminal device with which a user performs input by using a stylus pen (also called a touch pen or an electronic pen) is referred to as a pen tablet.
A pen tablet visualizes a trace made by a stylus pen by performing software processing. Specifically, in a pen tablet, a CPU generates a pen drawing image when a user performs pen input by using a stylus pen, and generates screen data corresponding to one frame by using a frame memory so that the screen data includes the pen drawing image. Screen data so generated is accumulated in the frame memory, is read from the frame memory at a predetermined refresh cycle, and is displayed on the touch panel (refer to Patent Literature 1).